Method of making an electrical assembly fastened with thermoplastic eyelet

ABSTRACT

The assembly includes at least two pieces of material, each having a hole therein aligned with the hole in the other piece of material, and a plastic eyelet positioned in the holes and having a radially extending flange on one end thereof which engages one piece of material and a rolled over rim at the other end thereof which engages the other piece of material to hold the pieces of material together. The method includes the steps of: assembling the pieces of material with a plastic sleeve positioned in the holes, the sleeve having the radially extending flange on one end with the other end of the sleeve extending beyond one piece of material; holding the flange against one piece of material while raising the temperature of the extending end of the sleeve above its softening temperature; and simultaneously shaping at least a part of the extending end of the sleeve into the rolled over rim which extends radially from the extending end of the sleeve and in abutment with the other piece of material.

ilnite States atent [1 1 Shea [ Aug. 28, 1973 [75] Inventor: Gerald J.Shea, Buffalo Grove, Ill.

[73] Assignee: Underwriters Safety Device Co.,

Chicago, Ill.

[22] Filed: July 29, 1971 [21] Appl. No.: 167,234

[52] U.S. Cl. 29/25.42, 24/73 P, 24/90 HA, 24/142, 29/512, 29/609,264/249, 317/261 [51] Int. Cl HOlg 13/00 [58] Field of Search 24/90 H,90 A, 141, 24/142, 73 P, 202; 29/25.42, 609, 512;

Primary Examiner-Charles W. Lanham Assistant Examiner-Carl E. HallAttorney-Fred S. Lockwood,.loseph P. OHalloran et al.

[571 ABS w: m

The assembly includes at least two pieces of material, each having ahole therein aligned with the hole in the other piece of material, and aplastic eyelet positioned in the holes and having a radially extendingflange on one end thereof which engages one piece of material and arolled over rim at the other end thereof which engages the other pieceof material to hold the pieces of material together. The method includesthe steps of: assembling the pieces of material with a plastic sleevepositioned in the holes, the sleeve having the radially extending flangeon one end with the other end of the sleeve extending beyond one pieceof material; holding the flange against one piece of material whileraising the temperature of the extending end of the sleeve above itssoftening temperature; and simultaneously shaping at least a part of theextending end oithe sleeve into the rolled over rim which extendsradially from the extending end of the sleeve and in abutment with theother piece of material.

5 Claims, 5 Drawing Figures Patented Aug. 28, 1973 INVENTOR GERALD J.SHEA METHOD OF MAKING AN ELECTRTCAL ASSEMBLY FASTENED WITH THERMO-PLASTIC EYELET The present invention relates to an improved assembly,and particularly to an electrical assembly, which is held together by aplastic eyelet. The invention also relates to a method for rolling overthe end of a thermoplastic sleeve extending through at least two piecesof material to form the sleeve into an eyelet for holding the pieces ofmaterial together.

Heretofore, metal eyelets have been widely used for fastening pieces ofmaterial together. Also in the recent past plastic rivets have been usedin assemblies for holding at least two pieces of material together. Inthis use of a plastic rivet one end of the rivet is heated and stakedover to hold two or more pieces together. Typically, an ultrasonicwelding device is utilized for staking over the end of the rivet.

The utilization of a plastic eyelet in place of a metal eyelet or ametal or plastic rivet has not been considered feasible since plasticmaterials do not have the requisite ductility to permit rolling over ofthe end of the sleeve to form the eyelet. In this respect, either theelasticity of the plastic material or the brittleness of the materialwould prevent adequate rolling over of the end of a plastic sleeve toform a plastic eyelet. In other words, for a soft plastic material therolled over portion of the sleeve would not retain the rolled over statebecause of the memory of the material and the rolled over portion wouldbend back toward, if not completely to, its original position. If theplastic material is brittle the rolled over portion would crack andwould not form a suitable annular collar for holding at least two piecesof material together.

if heat is used, one problem that is incurred is the inability tolocalize the heat at the end of the sleeve so that only the end of thesleeve is softened. Another problem is the proper forming or shaping ofthe softened end into a collar or rim extending radially outwardly fromthe central axis of the sleeve to form the eyelet. In view of theseproblems, the use of plastic eyelets has not appeared to be practical orfeasible.

Nonetheless, the use of a plastic eyelet in place of a metal eyelet hasa number of advantages. First of all, a plastic eyelet is usually formedfrom much less material than a plastic or metal rivet and therefore asaving of the plastic material is obtained. Secondly, in an electricalassembly where at least two pieces of insulating material are broughttogether with a piece of electrically conductive material interposedtherebetween and fastened together, it is desirable that no electricalcontact (short circuit) be made between the electrically conductivematerial and the fastening means such as an eyelet or rivet utilized forfastening the pieces of material together.

In the past, to minimize and hopefully to prevent such short circuitsthe hole in the conductive material was made larger than the holes inthe insulating material so that when the holes are coaxially aligned,the fastener extending between and secured in the holes of theinsulating material will not engage the larger circumference of the holein the conductive material. However, in many instances the conductivematerial can be moved relative to the pieces of insulating material sothat a portion thereof contacts the fastener and if the fastener is ametal eyelet the metal eyelet is raised to the potential of theelectrically conductive material. This can cause serious problems wherea mounting screw extends through the metal eyelet and is fastened to ametal base or wall in an electrical cabinet particularly where the baseor wall is at ground potential. Thus, when the electrically conductivematerials is shifted relative to the pieces of insulating material, thepiece of conductive material may come in contact with the metal eyeletand cause a short circuit.

Accordingly, in one preferred embodiment of the assembly of the presentinvention at least two pieces of material, each with a hole thereinaligned with the hole in the other piece of material, are held togetherby a thermoplastic eyelet received through the aligned holes. Theplastic eyelet is formed from a sleeve which has a projection extendingradially outwardly from one end of the sleeve. When the sleeve isinserted into the aligned holes the projection abuts against one of thepieces of material and the other end of the sleeve extends outwardlyfrom the other piece of material. The extending end of the plasticsleeve is rolled over to form the plastic eyelet and hold the two piecesof material together.

The method of the present invention for forming the above describedassembly includes the steps of bringing the two pieces of materialtogether with the holes therein aligned, inserting the thermoplasticsleeve into the aligned holes with the projection engaging one piece ofmaterial and the other end of the sleeve extending outwardly from thesecond piece of material, holding the projection against the one pieceof material while raising the temperature of the extending end of thesleeve above the softening temperature, and simultaneously shaping atleast a part of the extending end of the sleeve into a projectionextending radially from the sleeve and in abutment with the other pieceof material.

From the foregoing description it is apparent that a number ofadvantages can be obtained by fastening two or more pieces of materialtogether with a plastic eyelet. Accordingly, a primary object of thepresent invention is to provide an assembly which includes two pieces ofmaterial fastened together with a non-metallic eyelet.

It is another object of the present invention to provide the assemblydescribed in the preceding paragraph and in which the non-metalliceyelet is thermoplastic.

Another object of the present invention is to provide a method forforming the assembly described in the preceding paragraph wherein themethod includes the steps of raising the temperature of a projecting endof a thermoplastic sleeve above its softening temperature whilesimultaneously shaping at least a part of the projecting end of thesleeve into a projection extending radially from the sleeve.

Another object of the present invention is to provide a method asdescribed in the preceding paragraph wherein the step of raising thetemperature of the projecting end of the sleeve is accomplished bybringing the tip ofa shaping tool into contact with the projecting endof the sleeve while vibrating the tip.

Another object of the present invention is to provide a method of thetype defined in the preceding paragraph wherein the tip of the shapingtool has an annular groove therein which is adapted to come into contactwith the extending end of the sleeve.

Another object of the present invention is to provide a method of thetype defined in the preceding paragraph wherein the outer edge of theannular groove is defined by an annular ring which engages one of thepieces of material when the tool is brought into contact with theprojecting end of the sleeve to prevent flash when the temperature ofthe projecting end of the sleeve is raised to its softening point.

Another object of the present invention is to provide a method of thetype described in the preceding paragraph wherein the shaping tool has acentral axis, the groove is concentric with the axis and the tip of thetool includes a central projection located on the central axis.

Still another object of the present invention is to provide anelectrical assembly comprising at least two pieces of insulatingmaterial and at least one piece of electrically conductive materialwhich is interposed between the two pieces of insulating material and inwhich assembly the pieces of material are held together by a plasticeyelet.

For a more complete understanding of the nature and scope of the presentinvention reference may now be had to the accompanying drawings wherein:

FIG. 1 is an elevational view of a portion of an electrical assembly asit is being fastened together by plastic eyelets and an ultrasonicassembly in position to form a plastic sleeve into a plastic eyelet;

FIG. 2 is an enlarged fragmentary view, partially in section, of thesleeve shown in FIG. 1 and the tip of the ultrasonic assembly;

FIG. 3 is a view similar to FIG. 2 showing the position of the tip ofthe ultrasonic assembly when it is brought into contact with theextending end of the sleeve;

FIG. 4 is a top plan view of the sleeve and assembly shown in FIG. 2 andtaken along line 4.4 of FIG. 2; and

FIG. 5 is a top plan view similar to FIG. 4 and showing the sleeve afterit has been rolled over, and is taken along line 55 of FIG. 3.

Referring now to the drawings in greater detail, a laminated electricalassembly is generally indicated at in FIG. 1 and includes five pieces orstrips of material 11-15. The strips of material 11, 13 and are made ofan insulating material and the intermediate strips 12 and 14, interposedbetween the strips 11 and 13 and 13 and 15, respectively, are made of anelectrically conductive material.

The assembly 10 also includes a plurality of connector tabs which extendfrom each of the strips of electrically conductive material 12 and 14 oneither side of the laminated assembly 10. One of the connector tabsextending from the strip 12 is generally indicated at 16 in FIG. 1 andextends from the side of the laminate 10 hidden from view in FIG. 1, andone of the connector tabs which extends from the strip 14 is indicatedat 18. End views of several of the connector tabs 16 and 18 are shown inFIGS. 4 and 5.

According to the teachings of the present invention the laminate 10formed from the pieces of material 11-15 are held together by plasticeyelets, one of which is shown at 20 in FIG. 1. Each eyelet 20 is formedfrom a thermoplastic sleeve 22. In FIG. 1, one such. sleeve 22 is shownin position beneath an ultrasonic assembly or welder 24. The ultrasonicassembly 24 is conventional and of known type having a body portion 26and a welding horn 28. However, the tip 30 of the welding horn 28 has anovel configuration which enables the horn 28 to be utilized in rollingover one end of the plastic sleeve 22 to form the eyelet 20 as will bemore fully described in connection with FIGS. 2-5.

As shown in FIG. 2 each of the strips 11-15 has a hole therein sized toreceive the plastic sleeve 22. These holes are indicated respectively at31-35. It will be understood that when the laminated electrical assembly10 is formed, the strips 11-15 are brought together with the holes 31-35aligned for receiving the sleeve 22.

The sleeve 22 is sized to fit in the aligned holes 31-35 and has aradially extending projection or annular collar 23 which extends fromone end 38 of the sleeve 22. Also, the sleeve 22 has a length which isgreater than the width of the laminate formed by the strips 31-35 sothat the other or second end 36 of the sleeve 22 extends beyond theouter surface 37 of the strip 11. The shape of the end 36 of the sleeve22 before it is rolled over" is best shown in FIG. 4.

In the enlarged view of FIG. 2 it is apparent that tip 30 is threadedand is secured in a mating threaded recess 39 in horn 28. Hence, in theillustrated embodiment, tip 30 is replaceable, in keeping with generallyaccepted practice, and this permits worn tips 30 to be replacedinexpensively. More importantly, perhaps, this feature makes the presentinvention readily and inexpensively adaptable to existing equipmenthaving the replaceable tip feature.

The novel tip 30 includes an annular groove 40 which is adapted to comeinto contact with the extending end 36 of the sleeve 22 for shapingand/or forming a portion of the extending end 36 into a rolled over,annular projection or collar thereby forming the sleeve 22 into theeyetlet 20 as will be hereinafter more fully described. The groove 40 isrounded and partially circular in cross section. The outer edge of thegroove 40 is defined by an annular ring 42 which in the preferredembodiment shown in FIGS. 2 and 3 has a rounded surface 43.

The groove 40 and the ring 42 are coaxial with the central axis 44 ofthe tip 30 and horn 28, and the inner edge of the groove 40 is definedby the side of a projection 48 which extends outwardly from the tip 30of the horn 28 on the central axis 44 of the horn 28 and tip 30.Preferably and as shown in FIGS. 2 and 3 the projection 48 has a roundedend 50.

With reference to FIG. 3 of the drawings, the method of the presentinvention for fastening the pieces or strips of material 11-15 togetherwith the thermoplastic eyelets 20 includes the steps of: bringing thepieces 11-15 together with the holes 31-35 aligned, inserting into thealigned holes 31-35 the thermoplastic sleeve 22 with the projection orcollar 23 at the one end 34 of the sleeve 22 in abutment with the strip15 and with the other end 36 of the sleeve 22 extending outwardly fromthe strip 11, holding the projection or collar 23 against the strip 15while raising the temperature of the extending end 36 of the sleeve 22above its softening temperature and simultaneously shaping at least apart of the extending end 36 of the sleeve 22 into a projection orannular collar 52 extending radially from the sleeve 22 and in abutmentwith the strip 11. Preferably, the steps of raising the temperature ofthe end 36 and shaping the end 36 are accomplished by bringing the tip30 into engagement under pressure with the end 36 of the sleeve 22 whilevibrating the tip 30 at a high frequency such as for example at about20,000 cycles per second.

As best shown in FIG. 3 when the tip 30 is brought into engagement withthe extending end 36 of the sleeve 22 the end 36 is received in andshaped by the annular groove 40 as the tip 30 is pressed downwardlyuntil the annular ring 42 on the tip 30 engages the surface 37 on thestrip 31. This engagement between the ring 42 and the surface 37 of thestrip 11 prevents the formation of flash, that is to say, it preventssome of the softened thermoplastic material at the end 36 of the sleeve22 from flashing radially outwardly from the sleeve 22.

As shown in FIG. 3 the projection 48 extends into the interior of thesleeve 22 and this projection is preferred in the disclosedconfiguration of the tip 30 for the purpose of preventing the softenedend 36 of the thermoplastic sleeve 22 from collapsing inwardly of thesleeve when the end 36 is being heated and shaped by the vibrating tipto form the annular collar 52.

A top plan view of the rolled over annular collar 52 formed by rollingover a part of the end 36 of the sleeve 22 to form the eyelet 20 is bestshown in FIG. 5. As shown in FIGS. 3 and S, the projection 52 extendsradially from the end 36 of the sleeve 22 and is in abutment with thesurface 37 of the strip 11.

From the foregoing description of a preferred embodiment of theelectrical assembly of the present invention and the method for formingsame, it will be apparent that the teachings of the present inventioncan be utilized in other assemblies wherein it is desired to fasten atleast two pieces of material together with a non-metallic eyelet.Accordingly, the scope of the present invention is only to be limited asnecessitated by the accompanying claims.

I claim:

1. A method for making an electrical assembly including first, secondand third pieces of insulating material with first and second pieces ofelectrically conductive material positioned between said first andsecond pieces of insulating material and said second and third pieces ofinsulating material, respectively, said pieces of electricallyconductive material being provided with connector tabs by whichelectrical connections may be made thereto, each of said pieces ofinsulating material and conducting material having a circular holetherein each of said holes having substantially the same diameter, saidmethod including the steps of: bringing the pieces of material togetherto form a laminate having alternate layers of insulating and conductivematerial with the holes in all said pieces of material aligned;inserting into said aligned holes an insulating thermoplastic sleevehaving abutment means extending radially outwardly from one end of saidsleeve for engaging said first piece of insulating material, said sleevehaving substantially the diameter of the aligned holes, said sleevehaving a length greater than the combined thickness of said pieces ofmaterial so that the other end of said sleeve extends outwardly fromsaid third piece of insulating material when said abutment means engagessaid first piece of insulating material; holding said abutment meansagainst said first piece of insulating material while raising thetemperature of said extending end portion of said sleeve above itssoftening temperature; and simultaneously shaping at least a part ofsaid extending end of said sleeve into a projection extending radiallyfrom said sleeve and in abutment with said third piece of insulatingmaterial, thereby fastening said pieces together with said electricallyconductive pieces being insulated from each other and said connectortabs available for connection thereto.

2. The method of claim 1 wherein said assembly further includes at leastone additional piece of insulating material and at least one additionalpiece of electrically conductive material, the number of additionalpieces of insulating material being equal to the number of additionalpieces of conductive material, with respective pieces of conductingmaterial positioned between respective adjacent pieces of insulatingmaterial and said sleeve has a length greater than the combinedthickness of the laminate formed by said pieces of insulating materialand said pieces of conducting material so that said other end of saidsleeve extends beyond one side of said laminate.

3. The method of claim 1 wherein the temperature of the extending endportion is raised and the simultaneous shaping thereof is accomplishedby bringing a shaping element axially against said extending end portionof said sleeve, and vibrating said shaping element at ultrasonicfrequency sufficient to heat and shape the extending end portion.

4. The method of claim 3 wherein said assembly further includes at leastone additional piece of insulating material and at least one additionalpiece of electrically conductive material, the number of additionalpieces of insulating material being equal to the number of additionalpieces of conductive material, with respective pieces of conductivematerial positioned between respective adjacent pieces of insulatingmaterial and said sleeve has a length greater than the combinedthickness of the laminate formed by said pieces of insulating materialand said pieces of conductive material so that said other end of saidsleeve extends beyond one side of said laminate.

5. The method of claim 3 wherein said ultrasonic frequency is about20,000 cycles per second.

1. A method for making an electrical assembly including first, secondand third pieces of insulating material with first and second pieces ofelectrically conductive material positioned between said first andsecond pieces of insulating material and said second and third pieces ofinsulating material, respectively, said pieces of electricallyconductive material being provided with connector tabs by whichelectrical connections may be made thereto, each of said pieces ofinsulating material and conducting material having a circular holetherein each of said holes having substantially the same diameter, saidmethod including the steps of: bringing the pieces of material togetherto form a laminate having alternate layers of insulating and conductivematerial with the holes in all said pieces of material aligned;inserting into said aligned holes an insulating thermoplastic sleevehaving abutment means extending radially outwardly from one end of saidsleeve for engaging said first piece of insulating material, said sleevehaving substantially the diameter of the aligned holes, said sleevehaving a length greater than the combined thickness of said pieces ofmaterial so that the other end of said sleeve extends outwardly fromsaid third piece of insulating material when said abutment means engagessaid first piece of insulating material; holding said abutment meansagainst said first piece of insulating material while raising thetemperature of said extending end portion of said sleeve above itssoftening temperature; and simultaneously shaping at least a part ofsaid extending end of said sleeve into a projection extending radiallyfrom said sleeve and in abutment with said third piece of insulatingmaterial, thereby fastening said pieces together with said electricallyconductive pieces being insulated from each other and said connectortabs available for connection thereto.
 2. The method of claim 1 whereinsaid assembly further includes at least one additional piece ofinsulating material and at least one additional piece of electricallyconductive material, the number of additional pieces of insulatingmaterial being equal to the number of additional pieces of conductivematerial, with respective pieces of conducting material positionedbetween respective adjacent pieces of insulating material and saidsleeve has a length greater than the combined thickness of the laminateformed by said pieces of insulating material and said pieces ofconducting material so that said other end of said sleeve extends beyondone side of said laminate.
 3. The method of claim 1 wherein thetemperature of the extEnding end portion is raised and the simultaneousshaping thereof is accomplished by bringing a shaping element axiallyagainst said extending end portion of said sleeve, and vibrating saidshaping element at ultrasonic frequency sufficient to heat and shape theextending end portion.
 4. The method of claim 3 wherein said assemblyfurther includes at least one additional piece of insulating materialand at least one additional piece of electrically conductive material,the number of additional pieces of insulating material being equal tothe number of additional pieces of conductive material, with respectivepieces of conductive material positioned between respective adjacentpieces of insulating material and said sleeve has a length greater thanthe combined thickness of the laminate formed by said pieces ofinsulating material and said pieces of conductive material so that saidother end of said sleeve extends beyond one side of said laminate. 5.The method of claim 3 wherein said ultrasonic frequency is about 20,000cycles per second.